An alcohol is an organic compound formed by replacing on or more hydrogen on an alkane with a hydroxyl functional group (- OH). The hydroxyl group should not be confused with the hydroxide ion does. It remains attached to a hydrocarbon group (R), giving the compound its set of properties that are associated with alcohols.
The name of the hydrocarbon group determines the name of the alcohol. If the hydrocarbon group in ROH is methyl, for example, the alcohol is called methyl alcohol. Using the IUPAC naming rules, the name of an alcohol has the suffix “-ol”. Thus, the IUPAC name of methyl alcohol is methanol. If the molecule has a sufficient number of carbon atoms to require further definition, the base name is determined from the longest continuous chain of carbon atoms that has the –OH. The location of the hydroxyl group is identified with a number.
All alcohols have the hydroxyl functional group, and all are chemically similar. Alcohols are toxic to humans, for example except that ethanol can be consumed in limited quantities. Consumption of other alcohols such as 2-propanol (isopropyl alcohol) can result in serious gastric distress. Consumption of methanol can result in blindness and death. Ethanol, C2H5OH, is produced by the action of yeast or by a chemical reaction of ethylene derived from petroleum refining. Yeast acts on sugars to produce ethanol and CO2. When beer, wine, and other such beverages are the desired products, the CO2, escapes during fermentation, and the alcohol remains in solution. In baking, the same reaction utilizes the CO2 to make the dough rise, and the alcohol is evaporated during baking. Most alcoholic beverages are produced by the yeast fermentation reaction, but some are made from ethanol derived from petroleum refining.
The hydroxyl group is strongly polar, and alcohols with six or fewer carbon atoms per molecule are soluble in bothalkanes and water. A solution of ethanol and gasoline is called gasohol. Alcoholic beverages are a solution of ethanol and water. The proof of such a beverage is double the ethanol concentration by volume. Therefore, a solution of 40 percent ethanol by volume in water is 80 proof, and wine that is 12 percent alcohol by volume is 24 proof. Distillation alone will produce a 190 proof concentration, but other techniques are necessary to obtain 200 proof absolute alcohol. Denatured alcohol is ethanol with acetone, formaldehyde, and other chemicals in solution that are difficult to separate by distillation. Since these denaturants make consumption impossible, denatured alcohol is sold without the consumption tax.
Methanol, ethanol, and isopropyl alcohol all have one hydroxyl group per molecule. An alcohol with two hydroxyl groups per molecule is called a glycol. Ethylene glycol is perhaps the best known glycol since it is used as an antifreeze. An alcohol with three hydroxyl groups per molecule is called glycerol (or glycerin). Glycerol is a by-product in the making of soap. It is added to toothpastes, lotions, and some candies to retain moisture and softness. Ethanol, ethylene glycol, and glycerol are compared in.
Glycerol reacts with nitric acid in the presence of sulfuric acid to produce glyceryl trinitrate, commonly known as nitroglycerine. Nitroglycerine is a clear oil that is violently explosive, and when warmed, it is extremely unstable. In 1867, Alfred Nobel discovered that a mixture of nitroglycerine and siliceous earth was more stable than pure nitroglycerine but was nonetheless explosive. The mixture is packed in a tube and is called dynamite. Old dynamite tubes, however, leak pure nitroglycerine that is again sensitive to a slight shock.
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